An enormous amount of data is accumulated everyday all over the world to accelerate the creation of big data, and some systems used for processing big data are constructed over a plurality of bases in overseas locations accompanied by long-distance communication. The amount of time for data transfer via a network between locations is thus not ignorable.
For example, when communication between locations is executed in accordance with a transport layer protocol (transmission control protocol (TCP)) in order to ensure communication reliability, an ACK packet for use in reception acknowledgement is transmitted, for a packet transmitted from a transmitter, from a receiver. If the ACK packet does not reach the transmitter within a time-out period, communication control for setting the time-out period to a long period and reducing a packet transmission rate is executed in order to reduce a packet loss and congestion. That is, control for reducing a throughput of communication is executed. A delay in a network affects not only a packet transmitted from a transmitter but also the ACK packet, and therefore, in a system accompanied by long-distance communication, a probability that the ACK packet does not reach the transmitter within the time-out period increases. Accordingly, in the system accompanied by long distance communication, a probability that the above-described communication control is executed increases and, even when communication reliability is ensured, communication efficiency might be reduced.
Then, there are cases where communication speed is increased using a wide area network (WAN) speed-increasing device. For example, WAN speed-increasing devices are arranged as a pair such that a WAN provided between locations between which communication with a long delay and a high discard rate is performed is interposed between the WAN speed-increasing devices, and increase the speed of communication between the locations using a unique protocol which is different from that of TCP communication. In this case, a transmitter transmits packets at a transmission rate which does not depend on an ACK packet but, in order not to cause congestion in the network between the WAN speed-increasing devices, the transmitter is controlled to transmit packets at a transmission rate in accordance with a usable bandwidth of the network. There might be cases where, if the transmitter continuously transmits packets without consideration of the usable bandwidth of the network, packet communication with a data amount exceeding an acceptable amount occurs in the network shared for another communication, and thus, congestion occurs in the network and thereby causes a packet loss in each communication.
In order to realize highly efficient and stable communication, circuit measurement in which a usable bandwidth which may be used in a network is executed and control of a transmission rate is performed.
For example, a technology in which, when the reception interval of measurement packets is equal to the transmission interval thereof, a transmission rate corresponding to the transmission interval is determined to be the usable bandwidth of a network has been known. Also, there has been another known technology in which, when a part of a plurality of packets burst-transmitted from a data transmitting unit is discarded, an output cycle of data burst is reduced in order to maintain a maximum output rate.
Japanese Laid-open Patent Publication No. 2011-182015, Japanese Laid-open Patent Publication No. 2006-74773, and Japanese Laid-open Patent Publication No. 2012-5087 describe the related techniques.